The known methods for monitoring trafficways are generally distinguished by the use of different types of sensors which are either embedded in the pavement of the roadway (invasive sensors) or are arranged above the roadway (noninvasive sensors). Invasive sensors require a high outlay for installation and must be exchanged from time to time as the roadway pavement wears. Moreover, they are only suitable for stationary arrangements. The trafficway monitored by them is limited by the arrangement of the embedded sensors.
In EP 2 048 515 A1, instead of embedding a sensor at a predetermined location in each individual lane of the multiple-lane roadway, a radar beam is directed substantially horizontal to the roadway and along the edge of the roadway across all of the lanes of the roadway. For this purpose, an angle-resolving radar device (FMCW radar device) for transmitting and receiving radar radiation is positioned relative to the roadway such that it transmits a radar beam forming a radar lobe with a beam width of between 20° and 40° at a horizontal setup angle of the radar beam axis (line of symmetry of the radar lobe) relative to the roadway edge of less than 45°. The radar device can be arranged in such a way that when driving through the radar lobe the vehicles either drive toward the radar device (oncoming traffic, front-measuring radar device) or away from the radar device (receding traffic, rear end-measuring radar device). Here the monitored trafficway is determined with respect to its position and size by the position of the radar beam axis relative to the edge of the roadway and by the beam width of the radar lobe.
According to EP 2 048 515 A1, cited above, the relative position of the vehicle with respect to the radar device which changes over the measurement duration is derived from the radar signals reflected by a vehicle as it drives through the radar lobe. When the relative position of the stop line with respect to the radar device is known, the relative position of the vehicle with respect to the radar device can be used to determine the perpendicular distance of the relative position from the stop line at a plurality of measurement times. Subsequently, the point in time at which the stop line is passed can be deduced from the velocity of the vehicle in question, which velocity has also been derived, and from the perpendicular distance of the relative positions from the stop line, and a photograph is taken if this time point does not occur within the green-light phase of a traffic light associated with the stop line.
The position of the vehicle associated with every measurement time is defined here by the position of a so-called point of impingement for which a distance and an angle are determined from the reflection signals in each instance.
For oncoming traffic where the front end of the vehicle lies in the reflection region of the radar beam, the aforementioned method allows a reliable detection of traffic infractions at a traffic light, since the front end of the vehicle, which is naturally the first to pass the stop line, substantially determines the position of the so-called point of impingement.
For receding traffic where only the rear end of the vehicle is still located in the reflection region of the radar beam with increasing proximity to the stop line and the rear end of the vehicle accordingly substantially determines the position of the so-called point of impingement, there is no detection of traffic infractions where the front end of the vehicle, but not the rear end of the vehicle, passes the stop line at a point in time depending on a given switching state of the traffic light.